Support zsh (and other non-bash shells) as the tmux session shell

[dajaxx]

Problem

Persisterm hardcodes bash as the shell inside tmux sessions (tmux.ts line 111):

set-option -g default-command "bash --rcfile ${CONFIG_SHELL_INIT}"

And uses PROMPT_COMMAND (bash-only) for the IPC socket refresh hook (lines 249-256).

Proposed fix

1. Use $SHELL -l (login shell) instead of hardcoding bash --rcfile. Let the shell handle its own rc sourcing:

   set-option -g default-command "$SHELL -l"

2. Inject the _persisterm_refresh hook using shell-appropriate syntax:
   • bash: PROMPT_COMMAND (current behavior)
   • zsh: add-zsh-hook precmd _persisterm_refresh
   • fish: function _persisterm_refresh --on-event fish_prompt